Optimized formulation of diammonium glycyrrhizinate sustained-release tablet by BOX-Behnken design Determination of related substances in Diammonium Glycyrrhizinate Enteric Coated Tablet by LC-MS Preparation and pharmacodynamic evaluation of diammonium glycyrrhizinate-loaded chitosan nanoparticles Transmembrane transport and metabolism of diammonium glycyrrhizinate across rat small intestine in Ussing Chamber